This invention relates to a telephone conference circuit using digital techniques.
A telephone conference circuit provides conferencing by summing all the voice signals of plural conferees and transmitting the resultant signal to the conferees. In order to prevent the voice of a talker from being transmitted back to himself, the voice signal of the talker is excluded when summing up all the voice signals from the other conferees to produce a conference voice signal. One example of such a conference circuit is shown in U.S. Pat. No. 4,224,688 issued on Sept. 23, 1980 to Carmine A. Ciancibello et al. However, since the circuit proposed therein needs an input and an output terminals separately, the number of necessary wires becomes large to make the system bulky as well as costly.